1. Field of the Invention
The invention relates to a method for the application of liquid samples to a gel type electrophoresis medium for subsequent separation by electrophoresis.
2. Description of the Prior Art
The use of porous gel media for electrophoresis has become significant in recent years, particularly slides or plates of agar and agarose gel. For example, procedures have been described using agarose gel which permit the separation of as many as 15 or 20 different protein-containing samples into their components simultaneously by electrophoresis in about an hour. While such procedures are known and are also useful, the application of samples to gel electrophoresis media has heretofore been a significant problem. The most common prior method was to form wells or slits in the gel surface either by forming them as the gel was formed or cutting the wells into the gel after formation. The liquid sample containing the materials to be separated by electrophoresis was placed in the well and electrophoresis was carried out in the normal fashion. This technique of forming the gel around a well-forming member as the gel is applied to the slide is described for example by B. G. Johansson in "Agarose Gel Electrophoresis", Scand. J. Clin. Lab. Invest. 29, Suppl. 114, Page 7 et seq, at page 10. One problem with this technique is that it leaves a "sample application artifact" in the completed electrophoretic pattern. If the stained pattern is scanned with automatic instrumentation to determine relative or absolute concentrations of the separated fractions, the results must be corrected to remove the effect of this sample application artifact. Further, the presence of the wells results in a discontinuity in the gel thickness with resulting higher current density in the gel below the well during electrophoresis. This higher current density in turn causes localized heating and drying of the gel media during electrophoresis.
Another problem with application of samples to wells cut in the gel media is that the wells had to be wide enough to accept a full drop. Such wells resulted in application areas which were not as narrow as might be desired.
To remedy this problem some workers in the field have attempted to place a mixture of gel and a predetermined amount of sample in the previously formed well. This is obviously a laborious and therefore expensive procedure.
Other application techniques that have been attempted include application of the sample to a carrier of paper, thread or cellulose strips and then applying the carrier with the sample thereon to the gel surface.
Another technique which has been used is the stab-application technique in which the sample is applied to the end of a pointed instrument, which is then inserted into the gel. As the instrument is removed the sample remains in the gel.
A further method which has been developed is the so-called "wire-pull" method in which the gel is formed in a frame with side walls. A wire supported by openings in the frame side walls is embedded in the gel. The sample is placed in contact with one end of the wire extending outside the frame. The wire is then pulled through the gel from the end opposite to that having the sample thereon and the sample is pulled into the gel as the wire passes through the gel.
From the foregoing it is apparent that no simple wholly satisfactory method of sample application to gels such as are used in electrophoresis has heretofore been developed.